How do we match the same quantity to different number of digits (9 or 10)? Why do we count 0 if 0 is nothing? Here is a bonus lesson: Stick and Stake.
Imagine, at the previous page, you point at the bottom token and say zero. Can you point at the next token and say one? You can if words are token names. Otherwise, zero isn't a token. It's nothing.
Imagine now you point right below the bottom token. OK, it's 0. No tokens under this one. Then, the point between this token and the next token is 1, etc.